code: def check_basic_steps(graph):
      msg = "Add %s *%s* step in your flow."
      for prefix, node in (("a", "start"), ("an", "end")):
          if node not in graph:
              raise LintWarn(msg % (prefix, node))
  
imports: import re
  from .exception import MetaflowException
  from .util import all_equal
label_desc: Use image node_id 2 for calling a global function with example usage: check_basic_steps(graph) without return types